Electromagnetic position indicating device



United States Patent O 3,11fi,139 ELECTRGMAGNE'HS ESlTiN iNDiCATiNG BEY/'ECE Howard D. Warshaw, San Jose, alii., and Kenneth E.

Waltetieid, Princeton, NJ., assignors, by mesne assignments, to the United States ot America as represented by the Secretary of the Army Filed Feb. 23, 1962, Ser. No. 175,3@ 2 Claims. (Cl. 340-196) This invention relates to a position indicating device, and more particularly to an electromagnetic position indicating device for indicating a linear or angular position with a high degree of accuracy.

In the prior art it is known to use a position indicating mechanism consisting of a make and break switching circuit connected to a movable member whose position is to be monitored. The switching circuit usually has a contact brush in contact with a xed circular surface comprising a series of contact strips separated from one another electrically and connected respectively in the circuits of a plurality of indicator elements such as, for example, electric lamps. Any movement of the movable member will cause the contact brush to close the circuit between one of the contact strips and a lamp, thereby causing the lamp to light and indicate, to some degree, the position of the movable member. One diiculty with this type of position indicating device is that the contact friction between the brush and circular contact strips causes an undesired loading or damping of the movable member. Another disadvantage is that the switching circuit has a relative short life and requires constant maintenance.

Accordingly, it is an object of this invention to provide a position indicating device having no contacting surfaces, thereby greatly reducing the loading of the movable member and extending the operational life of the device.

Another object of this invention is to provide an improved indicating device which is not unduly large or complex.

Still another object of this invention is to provide an indicating device of the electromagnetic type which gives greater accuracy than heretofore obtainable.

A further object of this invention is to provide an indicating device of the electromagnetic type which does not depend on a constant supply voltage or frequency.

A still further object of this invention is to provide an electromagnetic position indicating device which is not affected by changes in external conditions surrounding the device nor by the position in which the device is mounted or placed.

In accordance with the invention, the electromagnetic position indicating device is provided with a magnetic core having a primary winding secured thereto. The primary winding is connected to a signal source which energizes the winding so as to produce a magnetic flux in the mag-V etio core. The magnetic core is provided with a plurality of fixed, parallel laminated strips upon which is wound a secondary coil. These secondary coils are connected in pairs in such a manner that the voltage in each coil is of opposite polarity in respect to the other coil. The magnetic core is also provided with a movable arm which is constructed of magnetic material and which is adapted to move in relationship to the lzuninated strips. The movable arm is attached to a movable member whose position is to be monitored. The pairs of secondary coils are attached to an indicating device through a switching circuit which is adapted to select which pair of coils is to be in circuit with the indicator device at any given time. Any movement of the movable member will be transmitted to the movable arm causing the arm to move and thereby change the magnet coupling through the strips. This change in magnet coupling will cause a corresponding FPice l change in the voltage fed to the indicating device by the secondary coil, thus giving an indication of the position of the movable member.

The novel features of this invention as well as the invention itself, both as to its organization and method of operation, will best be understood from the following description, when read in connection with the accompanying drawing, in which like reference numerals refer to like parts, and in which:

FIGURE 1 is a diagrammatic view illustrating one form of the electromagnetic position indicating device;

FIGURE 2 is an enlarged view of a portion of FIG- URE l;

FIGURE 3 is a graphic illustration of the wave forms explanatory of functions to be described in connection with the above gures; and

FlGURE 4 illustrates an alternative arrangement of the electromagnetic position indicating device.

In FIGURE l, the reference charger 1 designates generally ari electromagnetic position indicating device. The common magnetic core 2 of the device is constructed of a magnetic material such as, for example, several laminations of magnetic steel. A portion of the magnetic core 2 is formed by a plurality of xed, parallel strips 311-311. These strips are constructed of magnetic material and are preferably formed of several layers of laminations as is well known in the art. A movable arm or core portion 4 is secured to the common magnetic core 2 by a pivot joint S which allows the arm to rotate about the pivot point. The movable arm is constructed of magnetic matcrial which is, preferably, of the laminated type. The arm i has a cross sectional area such that the greater portion of the magnetic flux through the arm is linked only to one laminated strip when the arm and strip are juxtaposed in end to end relation. The extreme end ia of the movable arm 4 moves in an arc formed by the faces or ends of the parallel laminated strips 15a-3h While the other extreme end of movable arm 4 is provided with a nut 6 and threaded shaft portion 7. By properly adjusting the nut upon the threaded shaft, the movable arm may be balanced. If desired, this balancing arrangement may be omitted or replaced by other balancing devices as are well known in the art. A movable member 8, Whose angular position is to be monitored, is connected to the arm Lt by connecting means 9 in such manner that any angular movement of member 8 will cause arm 4 to rotate about pivot 5 thereby causing end 4a to move in relationship to the fixed laminated strips Srl-3h.

Wound aroundthe strips of the common magnetic core 2 is a primary or energizing coil 1d which is connected to a signal source 11 by connecting leads 12. The signal source i1 may be, for example, an electronic signal generator operating at a frequency between 1,000 and 20,00() cycles per second. Wound around each of the laminated strips 3a-3h is a secondary coil 13a-13h with each of said coils being spaced from the end of their respective laminated strips so as to form an arc as shown by FIGURE 1. The coils 13a-13h are grouped into adjacent pairs 13a-b, 13o-d, 13e-L 13g-h and are connected together so that the voltage produced by each coil is opposite in sign with respect to the voltage produced by the other coil of the pair. One lead from each pair of coils 13a-b, 13e-d, 13e-f, 13gh is connected to a common conductor 14 while the other lead is connected to conductors 1.5-1.8, respectively.

The common conductor 14 is connected directly to one terminal of an indicating device 2th which may be, for example, a vacuum tube voltmeter. The conductors l-it are connected to various terminal contacts of a switch 19 so that, by adjusting the movable contact ofthe switch 19, various pairs ot .the secondary coils may be switched into circuit with the indicator Ztl.

In understanding the mode of operation of the electro` magnetic position indicating device l, assume that the signal source Ill is operating to produce a magnetic flux in the common magnetic core 2 and that the movable member 8 is so located that the movable arm d is positioned between the laminated strips Sie-3f. The switch circuit 19 is adjusted so as to connect conductor 17 in circuit with the indicating device thereby establishing an electrical circuit through coils le-y, conductor I?, indicator device Zt? and the common conductor 1d.

As stated above, the secondary coils are arranged in adjacent pairs, the coils of each pair being so coupled together that the voltage induced in each coil is of opposite polarity from the voltage induced in the other coil. The reversing of the polarity of the voltage induced in each adjacent coil may be accomplished by winding the coils in reverse one from the other or, if the coils are wound in the same direction, by properly cross connecting the two coils together.

With the movable arm 4 equally positioned between laminated strips 31e-322 the magnetic coupling pat through the arm, laminated strips le-3f, and common magnetic core 2 will be equal, The voltage thus induced in the secondary windings 13e-13j by the change in magnetic linx, produced by the generator il, will be equal in amplitude but opposite in polarity. These voltages, being equal in amplitude but opposite in polarity, will effectively cancel one another and give no reading on the indicator 29. The absence of any voltage indicates that the movable arm is exactly positioned between the laminated strips .9e-3f as shown by point A on the graph of FIGURE 3.

Now assume that the movable member 8 is relocated so as to move arm d closer to the face of laminated strip 3e as shown by FIGURE 2. It becomes obvious that the magnetic coupling between the laminated strip 3e and movable arm d will become greater and that the voltage produced in the secondary winding 13e will increase while the magnetic coupling between the laminated strip 3f and the arm a' will decrease causing a drop in the voltage produced in the secondary coil 13f. The opposing voltages produced by the two coils lSe-laf are no longer equal in amplitude and therefore will not cancel out. The voltage difference produced by totaling the voltages will be sensed by the indicator 2d which will indicate a movement of the member 8, This new position of the movable member is shown as point B on the graph of FIGURE 3.

FIGURE 3 shows the additional voltages produced by movement of the arm 4 to various positions between the laminated strips Saz-3h.

ln FIGURE 4, a modied form of the electromagnetic position indicating device 1 is shown in which like reference numerals refer to like parts as described in relation to FIGURES l and 2 above. In this ligure, the ends or faces of the laminated strips 13a-13h have been constructed in a common plane with the end of movable arm 2l. Arm 21 is supported by a bearing 22 and is adapted to slide freely in a linear manner. Coupled to the arm 2 through coupling means 23 is a linearly movable member Z4 which, when moved, causes arm 2l to move thereby indicating a change in position on indicator 29. Since there is no physical contact between the movable arm and the laminated strips, a housing means 25 may be inserted between the laminated strip faces and the movablearm to thereby seal a portion of the device without adversely affecting the operation of the indicator. Such a housing may be desirable under certain conditions in order to protect a part or all of the device from external conditions.

The device is not noticeably affected by stray fields of magnetic flux. However, if the device is subject to extreme stray lields of magnetic llux, the entire common magnetic core and movable arnrmay be housed in a shield enclo sure, or a proper choice of input frequency together with a suitable filter in the output circuit of the secondary coils would eliminate the ellect of the stray elds upon the device.

From the above description, it is apparent that our invention can -be utilized to indicate the position of a mechanism having either angular or linear travel. The device is inde-pendent of supply voltage and frequency over wide ranges and can be made virtually independent of pressure, temperature or position of mounting. There need be no physical lcontact Ibetween the movable arm and the stationary laminated strip, hence the movable arm and strips, if desired, may be isolated electrically, thermally, Ior separated Iby a diaphragm for atmospheric isolation. Also the absence of any physical Contact between -the movable arm and laminated strips prevents the movable member 'from being lunduly loaded.

While we have described our invention in its preferred embodiments, We desire that it is lbe understood that modicationis may be made and that no limitations are inten-ded other than may be imposed by the scope of Ithe appended claims.

What is claimed is:

l. Apparatus for indicating the position of a movable member comprising,

:a common magnetic core member having a plurality 'of pairs of strip finger-like projections thereon,

`the common magnetic core Ihaving a movable arm portion mounted to .be moved relative thereto,

4the movable arm being p'ositionable adjacent to a selected pair of the strip .finger-like projections whereby a magnetic circuit will `be established through the common magnetic core, through the movable arm and 4through the selected pair of strip linger-like projections back to xthe common magnetic core member,

means to induce an alternating magnetic llux in each ringer of the magnetic circuit,

and ,co-il means on each nger, connected in pairs, to

sense the llow of magnetic llux through each pair of strip-like finger projections, said coil means of the selected pair of fingers being connected together such that electric currents in the coils are equal but opposite in ldirection so as to cancel one-another rwhen magnetic lluX is flowing equally in each linger of a pair of projections, and such that electnic currents in lthe coils do not cancel and therefore there is a net flow of cunrent in the coils when 4the magnetic flux in one of the iin-gens of a pair exceeds that of the other llinger of the pair.

2. Apparatus as set `forth in claim l, and means to monitor current flow, and absence thereof, in the coils to thereby indicate the position of the movable arm relative to the pairs of strip linger-like projections.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,417 Conrad July 3, 1945 2,931,023 Quade Mar. 29, 1960 2,960,688 Prochaska Nov.` l5, 1960 

1. APPARATUS FOR INDICATING THE POSITION OF A MOVABLE MEMBER COMPRISING, A COMMON MAGNETIC CORE MEMBER HAVING A PLURALITY OF PAIRS OF STRIP FINGER-LIKE PROJECTIONS THEREON, THE COMMON MAGNETIC CORE HAVING A MOVABLE ARM PORTION MOUNTED TO BE MOVED RELATIVE THERETO, THE MOVABLE ARM BEING POSITIONABLE ADJACENT TO A SELECTED PAIR OF THE STRIP FINGER-LIKE PROJECTIONS WHEREBY A MAGNETIC CIRCUIT WILL BE ESTABLISHED THROUGH THE COMMON MAGNETIC CORE, THROUGH THE MOVABLE ARM AND THROUGH THE SELECTED PAIR OF STRIP FINGER-LIKE PROJECTIONS BACK TO THE COMMON MAGNETIC CORE MEMBER, MEANS TO INDUCE AN ALTERNATING MAGNETIC FLUX IN EACH FINGER OF THE MAGNETIC CIRCUIT, AND COIL MEANS ON EACH FINGER, CONNECTED IN PAIRS, TO SENSE THE FLOW OF MAGNETIC FLUX THROUGH EACH PAIR OF STRIP-LIKE FINGER PROJECTIONS, SAID COIL MEANS OF THE SELECTED PAIR OF FINGERS BEING CONNECTED TOGETHER SUCH THAT ELECTRIC CURRENTS IN THE COILS ARE EQUAL BUT OPPOSITE IN DIRECTION SO AS TO CANCEL ONE-ANOTHER WHEN MAGNETIC FLUX IS FLOWING EQUALLY IN EACH FINGER OF A PAIR OF PROJECTIONS, AND SUCH THAT ELECTRIC CURRENTS IN THE COILS DO NOT CANCEL AND THEREFORE THERE IS A NET FLOW OF CURRENT IN THE COILS WHEN THE MAGNETIC FLUX IN ONE OF THE FINGERS OF A PAIR EXCEEDS THAT OF THE OTHER FINGER OF THE PAIR. 